This invention relates to a method and apparatus using a light spot for recording and reproducing information on and from a track on a recording medium, and more particularly to an optical information retrieving system which minimizes an adverse effect of a track offset that may occur during recording and improves the characteristics of a tracking servo system at the time of recording. The present invention is preferably applicable to a write-once-read-many type optical disk apparatus capable of additional recording of information.
Such a write-once-read-many type optical disk apparatus can record a large amount of information on an optical disk by directing a light spot from an optical head toward the optical disk and locally fusing a recording film by the heat of the light spot thereby forming pits in the recording film. However, the write-once-read-many type optical disk apparatus has such a problem that, depending on the characteristics of the optical head and optical disk, information cannot be normally recorded when a track offset occurs during recording information.
As a tracking method applicable to such an optical disk apparatus, there is a push-pull method which attains tracking utilizing light reflected and diffracted from a track guide groove (a pre-groove). It is known that, when this push-pull method is used, tracking operation tends to become unstable if a track offset occurs due to inclination of an optical disk or movement of a light beam. Provision of correction marks such as mirror marks in each track guide groove so as to prevent the unstable tracking operation is described in U.S. Pat. No. 4,663,751 and U.S. patent application Ser. No. 870,944 now U.S. Pat. No. 4,751,695. Also, provision of correction marks such as prewobbled pits in each track guide groove is described in U.S. patent application Ser. No. 845,340 now U.S. Pat. No. 4,748,609. These methods intend to stabilize the tracking control by detecting a track offset component from the correction marks such as the mirror marks or prewobbled pits and adding or subtracting the detected track offset component to or from an output signal of a guide-groove-based tracking servo signal thereby correcting the tracking error. Further, U.S. patent application Ser. No. 071,183 now U.S. Pat. No. 4,807,210 proposes a method in which a tracking error attributable to a track offset component detected from correction marks such as mirror marks or prewobbled pits is corrected in the read mode only, and, in the write mode or erase mode, the correction marks are used for detection of a track offset component, and the recording operation and erasing operation are controlled depending on the output level of the track offset component so as to prevent erroneous recording of information or erroneous erasing or insufficient erasing of data recorded already.
However, none of the prior art disclosures described above refers to the problem of occurrence of a track offset attributable to a pulse-like increase in the intensity of the light spot emitted during recording information.